Large-area electronics based on polymeric semiconductors, for applications such as display systems, often require the deposition and patterning of solution processable polymeric materials over large areas. Various printing techniques have been used to achieve the deposition and patterning. However, each of these printing techniques suffers from a number of problems.
One polymeric material deposition method uses ink jet printing to deposit droplets of polymeric material. However, ink jet printing is a slow sequential process. Using multiple ink jet nozzles to print in parallel speeds up the process but also dramatically increases complexity and expense.
A second patterning method uses liquid embossing. A publication by Bulthaup et al., Applied Physics Letters 79 (10) 1525, (2001), describes depositing an “ink” on a substrate and patterning the ink in a liquid embossing process. In order to pattern the ink, a stamp displaces the “ink” and creates a reverse or negative image on the substrate relative to the pattern in the stamp. In addition, after removal of the stamp, the “ink” is still liquid and is cured before handling. The curing process reduces the robustness and throughput of the process. Furthermore, heating the substrate to cure the “ink” can also degrade the electrical properties of the embossed polymer.
S. Y. Chou in U.S. Pat. No. 5,772,905 describes using conventional embossing and nanoprint lithography to flow a thin film under a stamp to create a pattern. An anisotropic etching step, such as reactive ion etching (RIE), finishes the pattern definition. Conventional nanoprint lithography often involves exposing the patterned polymer to high temperatures, UV exposure and etching processes. These processes result in a harsh environment that potentially degrades the electrical properties of the polymeric semiconductor.
Still other techniques use a surface-energy pattern on a substrate to pattern a polymer. C. R. Kagan et al. in Appl. Phys. Lett. 79 (21) 3536 (2001) describes patterning self-assembled monolayers using such a surface-energy pattern. Such patterns are typically generated using surface energy modulation. However, use of such a system in electronic device fabrication is restricted to surfaces on which a self-assembled monolayer can be deposited (typically the noble metals such as gold or palladium). An additional coating step, typically accomplished through dip-coating the surface-energy pattern of the substrate over the entire substrate area is complex and slow, lowering throughput and yield.
Thus an improved method of patterning a polymer is needed.